1. Field of the Invention
The present invention relates to a variable valve timing control apparatus.
2. Description of Related Art
JP-A-2002-357105 (US 2002/0139332 A1) describes an oil-pressure drive type variable valve timing device for an engine, in which a rotation phase of a camshaft with respect to a crankshaft is locked into a predetermined lock phase when the engine is stopped. The rotation phase of the camshaft with respect to the crankshaft is defined as variable cam timing (VCT) phase. The lock phase is set into an approximately middle in a controllable range of the VCT phase, so as to enlarge a controllable range of the valve timing. The middle lock phase is set suitably for start-up of the engine. The engine is activated in a state where the VCT phase is locked into the middle lock phase using a lock pin. When the start-up of the engine is completed, an oil pressure is raised to an appropriate value. Then, the lock pin is retreated so as to unlock the VCT phase, and the VCT phase is moved to a target phase in accordance with an operation state of the engine using a feedback control. When a lock requirement is generated in engine stop time or in engine idling time, the VCT phase is locked into the middle lock phase by the lock pin.
JP-A-2011-032905 describes a lock control in which a VCT phase is locked into a middle lock phase after the VCT phase is moved to a target phase past the middle lock phase by a predetermined angle. That is, feedback control is performed, and then, a lock pin locks the VCT phase while the VCT phase returns toward the middle lock phase.
However, when a malfunction is generated in a system that controls the VCT phase, for example, when an actual VCT phase cannot be calculated by a break in a line that transmits a crank signal or a cam signal, the feedback control cannot be performed. In this case, because the VCT phase may be unable to be locked into the middle lock phase, start-up property of the engine may get worse at the next engine activation time.
In JP-A-2002-357105, a system to control the VCT phase has an advance restricting pin and a retard restricting pin, and at least one of the restricting pins is used as a lock pin. One of the restricting pins may stick to a retreat position while both of the restricting pins are controlled to project. One of the restricting pins may stick to a projection position while both of the restricting pins are controlled to retreat. Because the projecting pin may collide to an inner wall face of a restriction groove, strange sound may occur, or wear or breakage may occur in the pin or the groove.
Moreover, when an engine stall (failure) occurs, the engine stops without an engine stop command in very short time, so that the VCT phase may be unable to be locked into the middle lock phase. In this case, start-up property of the engine may get worse at the next engine activation time.